Decode plus sign in resource attributes

sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/ResourceConfiguration.java

@@ -11,14 +11,11 @@
 import io.opentelemetry.common.ComponentLoader;
 import io.opentelemetry.sdk.autoconfigure.internal.SpiHelper;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
-import io.opentelemetry.sdk.autoconfigure.spi.ConfigurationException;
 import io.opentelemetry.sdk.autoconfigure.spi.ResourceProvider;
 import io.opentelemetry.sdk.autoconfigure.spi.internal.ConditionalResourceProvider;
 import io.opentelemetry.sdk.autoconfigure.spi.internal.DefaultConfigProperties;
 import io.opentelemetry.sdk.resources.Resource;
 import io.opentelemetry.sdk.resources.ResourceBuilder;
-import java.io.UnsupportedEncodingException;
-import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.HashSet;
@@ -68,18 +65,13 @@ public static Resource createEnvironmentResource() {
   @SuppressWarnings("JdkObsolete") // Recommended alternative was introduced in java 10
   public static Resource createEnvironmentResource(ConfigProperties config) {
     AttributesBuilder resourceAttributes = Attributes.builder();
-    try {
-      for (Map.Entry<String, String> entry : config.getMap(ATTRIBUTE_PROPERTY).entrySet()) {
-        resourceAttributes.put(
-            entry.getKey(),
-            // Attributes specified via otel.resource.attributes follow the W3C Baggage spec and
-            // characters outside the baggage-octet range are percent encoded
-            // https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/resource/sdk.md#specifying-resource-information-via-an-environment-variable
-            URLDecoder.decode(entry.getValue(), StandardCharsets.UTF_8.name()));
-      }
-    } catch (UnsupportedEncodingException e) {
-      // Should not happen since always using standard charset
-      throw new ConfigurationException("Unable to decode resource attributes.", e);
+    for (Map.Entry<String, String> entry : config.getMap(ATTRIBUTE_PROPERTY).entrySet()) {
+      resourceAttributes.put(
+          entry.getKey(),
+          // Attributes specified via otel.resource.attributes follow the W3C Baggage spec and
+          // characters outside the baggage-octet range are percent encoded
+          // https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/resource/sdk.md#specifying-resource-information-via-an-environment-variable
+          decodeResourceAttributes(entry.getValue()));
     }
     String serviceName = config.getString(SERVICE_NAME_PROPERTY);
     if (serviceName != null) {
@@ -133,5 +125,52 @@ static Resource filterAttributes(Resource resource, ConfigProperties configPrope
     return builder.build();
   }
 
+  /**
+   * Decodes percent-encoded characters in resource attribute values per W3C Baggage spec.
+   *
+   * <p>Unlike {@link java.net.URLDecoder}, this method:
+   *
+   * <ul>
+   *   <li>Preserves '+' as a literal plus sign (URLDecoder decodes '+' as space)
+   *   <li>Preserves invalid percent sequences as literals (e.g., "%2G", "%", "%2")
+   *   <li>Supports multi-byte UTF-8 sequences (e.g., "%C3%A9" decodes to "é")
+   * </ul>
+   *
+   * @param value the percent-encoded string
+   * @return the decoded string
+   */
+  private static String decodeResourceAttributes(String value) {
+    // no percent signs means nothing to decode
+    if (value.indexOf('%') < 0) {
+      return value;
+    }
+
+    int n = value.length();
+    // Use byte array to properly handle multi-byte UTF-8 sequences
+    byte[] bytes = new byte[n];
+    int pos = 0;
+
+    for (int i = 0; i < n; i++) {
+      char c = value.charAt(i);
+      // Check for percent-encoded sequence i.e. '%' followed by two hex digits
+      if (c == '%' && i + 2 < n) {
+        int d1 = Character.digit(value.charAt(i + 1), 16);
+        int d2 = Character.digit(value.charAt(i + 2), 16);
+        // Valid hex digits return 0-15, invalid returns -1
+        if (d1 != -1 && d2 != -1) {
+          // Combine two hex digits into a single byte (e.g., "2F" becomes 0x2F)
+          bytes[pos++] = (byte) ((d1 << 4) + d2);
+          // Skip the two hex digits (loop will also do i++)
+          i += 2;
+          continue;
+        }
+      }
+      // Keep '+' as '+' (unlike URLDecoder) and preserve invalid percent sequences which will be
+      // treated as literals
+      bytes[pos++] = (byte) c;
+    }
+    return new String(bytes, 0, pos, StandardCharsets.UTF_8);
+  }
+
   private ResourceConfiguration() {}
 }

sdk-extensions/autoconfigure/src/test/java/io/opentelemetry/sdk/autoconfigure/ResourceConfigurationTest.java

@@ -19,8 +19,12 @@
 import io.opentelemetry.sdk.resources.Resource;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.stream.Stream;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 import org.mockito.junit.jupiter.MockitoExtension;
 
 @ExtendWith(MockitoExtension.class)
@@ -50,6 +54,36 @@ void customConfigResourceWithDisabledKeys() {
                 .build());
   }
 
+  @ParameterizedTest
+  @MethodSource("decodeResourceAttributesArgs")
+  void decodeResourceAttributes(String input, String expectedKey, String expectedValue) {
+    Map<String, String> props = new HashMap<>();
+    props.put("otel.resource.attributes", input);
+
+    assertThat(
+            ResourceConfiguration.createEnvironmentResource(
+                DefaultConfigProperties.createFromMap(props)))
+        .isEqualTo(Resource.create(Attributes.of(stringKey(expectedKey), expectedValue)));
+  }
+
+  private static Stream<Arguments> decodeResourceAttributesArgs() {
+    return Stream.of(
+        // Plus sign preserved
+        Arguments.of("food=cheese+cake", "food", "cheese+cake"),
+        // Percent-encoded space in resource attribute value decoded to space
+        Arguments.of("key=hello%20world", "key", "hello world"),
+        // Invalid percent encoding preserved
+        Arguments.of("key=abc%2Gdef", "key", "abc%2Gdef"),
+        // Incomplete percent encoding preserved
+        Arguments.of("key=abc%2", "key", "abc%2"),
+        // Percent at end preserved
+        Arguments.of("key=abc%", "key", "abc%"),
+        // Multiple percent encodings
+        Arguments.of("key=a%20b%2Bc%3Dd", "key", "a b+c=d"),
+        // No percent encoding
+        Arguments.of("key=plain-value", "key", "plain-value"));
+  }
+
   @Test
   void createEnvironmentResource_Empty() {
     Attributes attributes = ResourceConfiguration.createEnvironmentResource().getAttributes();